EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/78712
52 52 EW REFRACTIVE April 2012 Refractive editor's corner of the world Tools for accurate IOL calculations by Faith Hayden EyeWorld Staff Writer and Maxine Lipner Senior EyeWorld Contributing Editor "Get your facts first, then you can distort them as much as you please." Mark Twain here's a great misconception about modern refractive cataract surgery. If you've followed the Refractive corner of the world the last few months, it will come as no surprise when I tell you that we are not as good as we think we are. As a group, we refractive cataract surgeons like to believe 90-95% of the time we achieve the refractive outcomes we intended. After all, we purchased sophisticated diagnostic instruments that take the guesswork out of corneal and axial length measurements. Ad- ditionally, we ARE highly skilled small inci- sion phaco surgeons who can reproducibly remove a patient's cataract and replace it with a foldable capsular fixated intraocular lens virtually every time. But the reality is, modern technology and highly skilled sur- gery are not quite enough to deliver results all the time. While we are getting better and results are improving, there are still areas for us to improve, some of which will hope- fully be just around the corner. Until these advancements in diagnostic technologies and surgical techniques develop, there are fortunately some things we can do to opti- mize our outcomes. We also need to pre- pare our patients (and ourselves) for possible refractive enhancements that— let's face it—are a part of today's refractive cataract surgery practice. In this month's Refractive corner of the world, I am de- lighted to have one of the foremost experts in the field, whom I am pleased to call my friend, Warren Hill, M.D., shed some light on the subject matter. T Kerry Solomon, M.D., refractive editor Warren Hill, M.D. Dr. Hill doles out his best advice W hen it comes to refrac- tive outcomes, sur- geons may not be as good as they think they are. According to EyeWorld Monthly Pulse survey re- sults from March, 57% of 408 physi- cians polled believe they come within 0.5 diopters of the target re- fraction during routine cataract sur- gery at least 90% of the time. But as Warren Hill, M.D., East Valley Oph- thalmology, Mesa, Ariz., said, "There is no way in the world that could be accurate." EyeWorld sat down with Dr. Hill to get his take on physicians' false confidence and how to optimize tools and improve outcomes. EyeWorld: Why are the Monthly Pulse numbers so inflated? Dr. Hill: Physicians are just not track- ing their outcomes, and they proba- bly rely on their staff to tell them if there's a problem. … Maybe their staff only tells them about problems 5% of the time. They assume that everything else is correct. But a con- clusion such as that can only come from [people] who do not track their outcomes. It's an impossibility with current technology and current for- mulas for such a high percentage of surgeons to have results such as these. Most surgeons are probably in the mid- to high-70s for being within .5 D of the target refraction. Probably less than 1% of surgeons are at 95% accuracy, and probably about 6% of surgeons are within 15%, which is 85% accuracy. And then the vast majority of surgeons are in the 70s to very low 80s—80% to 85% within .5 D is an upper-tier practice. This doesn't have a lot to do with how careful and competent Dr. Hill performs free lens constant analysis for the Haigis, Holladay 1, SRK/T, and Hoffer Q formulas through his website Source: doctor-hill.com/physicians/download.htm surgeons are; it really is a limitation of technology. … A two-variable third-generation formula gets it right about 80% of the time if every- thing else is fine—if there are no problems with the keratometry or the axial length. But the difficulty is that a two-variable formula has to make broad assumptions with very limited information. For example, a formula like SRK/T, Holladay 1, or Hoffer Q can only get it right if the assumptions of the formula match the assumptions of the eye. And if the eye didn't read the textbook, so to speak, the eye may have an ante- rior segment that's different than the limited assumptions these older formulas make. When this is the case, the accuracy is going to be off by small or large amounts. EyeWorld: Is it OK not to be 85% accurate? What is a reasonable accuracy goal? Dr. Hill: Very few people are 85% ac- curate—very few—6%. Not only is it OK, it is what it is. You can't be ac- curate 100% of the time when the exercise doesn't allow it. In 2007, in the journal Eye [(2009) 23, 149-152; published on- line 24 August 2007] some investiga- tors in the United Kingdom [published] a study that has come to be known as the United Kingdom National Health Service Benchmark Standard. In this study, they pro- posed that an acceptable limit for accuracy for refractive outcomes fol- lowing cataract surgery was 55% of patients within .5 D and 85% of pa- tients within 1 D. That's the accept- able standard in the United Kingdom—55%. EyeWorld: What can physicians do to improve outcomes? Dr. Hill: If there was any one thing that a modern, up-to-date practice could do [it] would be to change from the third-generation two-vari- able formulas such as SRK/T, Hoffer Q, and Holladay 1 to, at the mini- mum, a formula like Haigis that uses three variables or one of the newer, more accurate theoretical formulas such as Holladay 2 or the Olson for- mula. And I think in the years to come we're going to see additional, more precise calculation methodolo- gies such as statistical-based engi- neering models. If my crystal ball is correct, I would predict that we will be dropping theoretical formulas and either going to variations of ray tracing or statistical-based engineer- ing models, and these old, tired, re- warmed vergence formulas are just going to drop by the wayside. EyeWorld: Besides formulas, what other key steps could practitioners take here? Dr. Hill: They could employ valida- tion criteria. Remember, a measure- ment is only as good as our ability to understand what it means. … If you have keratometry values that are all over the place, maybe one of them is right and the others aren't, and you need to have a criteria like for the IOLMaster [Carl Zeiss Meditec, Dublin, Calif.]—the valida- tion criteria are three measurements within 0.25 D in each of the princi- ple meridians. For the LENSTAR [Haag-Streit USA, Mason, Ohio], the validation criteria for keratometry